Supported chromium oxide catalysts are commonly employed to prepare polyolefins having desirable characteristics. Various supports for chromium oxide catalysts have been disclosed in the art. The particular support used for the chromium oxide strongly affects the properties of the polymer being formed. Silica supports have primarily been used due to their ability to form highly active polymerization catalysts. However, silica supports do not provide for the production of ultra high molecular weight polymers when hexavalent chromium is formed during the catalyst activation, which often occurs.
Aluminum phosphate supports are similar to silica supports in that they form highly active catalysts. However like the silica supports, they also do not have the ability to produce very high molecular weight polymers. Further, the polymers produced using the aluminum phosphate supports tend to contain relatively high amounts of long chain branching, which is not always a desirable property during processing of the polymer. A need therefore exists to develop a method for producing polyolefins having less long chain branching and higher molecular weights.